Sputter deposition is used extensively within the semiconductor industry to deposit thin metallic and non-metallic films or layers onto a semiconductor substrate. Cathode sputter deposition, in particular, is widely utilized and involves the use of a target of sputtering material which is to be deposited onto the surface of a substrate. The target is supported in a vacuum sputter deposition chamber in a position generally facing the surface of the substrate to be sputter coated with a layer of the target material. A negative potential is then applied to the target through a cathode support to produce an electric field proximate the target which causes electrons to be emitted from the target surface toward a remote anode such as the vacuum chamber. The emitted electrons ionize a sparse inert gas introduced within the chamber and positive gas ions are formed creating a plasma of high ion concentration. The positive ions are attracted to the negative target and the ions bombard the surface of the target, ejecting or sputtering small particles of the target material from the target. The particles of sputtering material emitted from the target surface strike and adhere to the surface of the substrate positioned opposite the target and thereby form a sputter film or layer.
The electrically disturbed nature of the ionized plasma produces an inherent amount of random plasma electrical noise. Accompanying the plasma noise is an inherent amount of electrical plasma arcing which occurs when the characteristic impedance of the plasma suddenly drops. When random arcing occurs within the plasma, the level of the sputtering current increases and detrimental amounts of electrical energy are randomly conducted through the plasma. The plasma arcing may occur in the plasma, between the plasma and the metal housing of the deposition chamber, between the target and the plasma or between the substrate and the plasma if the substrate is biased. Plasma arcing is caused by a variety of different factors. For example, arcing might be caused by flaking of the target during sputtering, overheating of the target, a gas disturbance within the plasma, or impurities in either the inert gas utilized to form the plasma or the target material. Inherently, plasma noise produces a certain amount of micro-arcing within plasma inside the deposition chamber. However, the micro-arcing may develop into more severe plasma arcing within the chamber.
Plasma noise, micro-arcing and severe arcing all adversely affect the quality of the sputter deposition coating. For example, the noise and arcing contributes to the deterioration of the film properties during deposition and may lead to substrate contamination and device damage on the substrate. Therefore, plasma noise and arcing reduces the yield of the sputter deposition process and reduces the overall productivity of sputtering equipment.
The source of plasma electrical instability in DC sputtering is a result of the plasma discharge and its interaction with the DC power supply which is utilized to originate the plasma. Therefore, the drawbacks of plasma noise and plasma arcing are inherent in DC sputter deposition regardless of the use of a metallic or non-metallic target or the use of a reactive gas for reactive sputter deposition. Noise and arcing problems also exist regardless of whether the substrate is electrically biased, or whether the target is biased with an additional RF source. Currently available commercial plasma DC power supplies utilized for sputter deposition do not adequately address the effects of plasma noise and arcing. Available power supplies only have the capabilities to detect the most severe arcing within the chamber, e.g., a stable DC current in excess of approximately 50-110 A. Such power supply detection circuits are not designed for plasma noise and micro-arcing but are utilized mainly for protecting the power supply during a detectable electrical short at the output. Upon detecting such a short or a continuous, severe arc, the power supply momentarily interrupts the output (i.e. 4-25 msec.) to eliminate the short or arc. The response time for conventional power supply detection circuits is generally in the range of 100-500 .mu.sec. However, plasma noise and plasma micro-arcs generally have a much shorter duration, and thus currently available plasma DC power supplies to not have the ability to respond to plasma noise/arcing current fluctuations having a frequency in the order of 1-10 MHz (i.e. a duration of 0.1-1.0 .mu.sec). As a result, currently available plasma DC power supplies are inadequate for controlling plasma noise and micro-arcing when utilized for sputter deposition and thus cannot reduce the resultant detrimental effects on the sputter deposited film.
Furthermore, currently available power supplies may actually exacerbate the problems associated with plasma arcing. For example, a DC power supply has a certain amount of electrical energy stored therein which is predominantly in the output stage of the power supply, such as in the output filter. Upon the existence of micro-arcing or arcing conditions, the stored energy may be discharged into the sputtering chamber. The discharged energy pulse has a duration of approximately 0.2-2 .mu.sec., which is too rapid to be controlled or limited by the detection circuitry of the power supply. The related in-rush currents of the discharged energy are in the order of 50-250 A and may adversely contribute to the development of arcing conditions within the plasma because the stored energy is essentially poured into or conducted through the fluctuating plasma. Therefore, currently-available plasma DC power supplies may actually contribute to the development of detrimental arcing conditions in addition to the existing plasma noise and micro-arcing.
Accordingly, it is an object of the present invention to reduce plasma noise and micro-arcing during DC sputter deposition to improve the electrical stability of the plasma and to thus yield improved sputter deposition of thin films. It is a further objective to reduce the contamination of the deposited films and the damage to the devices on a substrate due to plasma noise/arcing. It is a further objective of the present invention to control severe arcing conditions and to improve operation of the internal detection circuits of a DC power supply to reduce the detrimental effects of plasma arcing. It is a still further objective of the present invention to reduce plasma noise and arcing simply, inexpensively and efficiently without affecting the processing conditions and the biasing conditions of the cathode target.